Benefits of larval group feeding by Chrysolina aurichalcea asclepiadis on Vincetoxicum : improved host location or feeding facilitation?

Several studies have shown that group feeding by immature insects enhances larval performance through feeding facilitation. However, the benefits of this behavior have not been studied for species that hatch off from their host plant. For these taxa, group feeding may enhance recruitment of newly emerging larvae and may improve larval performance through feeding facilitation. I conducted laboratory experiments with the European chrysomelid Chrysolina aurichalcea asclepiadis (Villa) (Coleoptera: Chrysomelidae: Chrysomelinae), whose larvae hatch on the ground near their host plant [ Vincetoxicum (Apocynaceae)] and feed in groups during early instars, to determine whether cues associated with larval feeding enhance neonate establishment and determine whether feeding in groups improves larval performance. Neonates located shoots infested with larvae more often than when confined to shoots with leaves that were undamaged or mechanically damaged. When provided a choice, neonates preferred shoots infested with 10 larvae to non‐infested shoots and shoots with one or five larvae. In the larval performance test, group feeding did not improve survival, but larvae completed larval development about 2 days faster when larvae were raised in groups of 10 compared to isolated larvae. However, larval group size negatively affected the size of emerging adults. The results of this study indicate that the main benefit of group feeding is to young C. a. asclepiadis larvae and this benefit diminishes over development due to competition of mature larvae.